Cylinder injection engine and method of combusting engine

ABSTRACT

A direct injection engine capable of direct injection of fuel into a combustion chamber characterized in that discharge of gas containing hazardous gas component such as HC can be reduced and fuel economy can be improved by stratified charge combustion in the operation range of low to high speeds. Spray fuel from the fuel injector is fed to the ignition plug by tumble air flow generated in the combustion chamber and formed between the fuel injector located on the side of the combustion chamber and the ignition plug installed on the top of the combustion chamber. This engine (a tumble guide direct injection engine) is configured to ensure that fuel reaches the ignition plug at the time of its ignition.

TECHNICAL FILED

The present invention relates to a direct injection engine, particularlyto a direct injection engine wherein fuel is directly injected into thecombustion chamber for forming a tumble air flow.

BACKGROUND ART

According to the prior art, a direct injection engine is proposedwherein an injection nozzle of the fuel injector is provided in thecombustion chamber of the engine, and fuel is injected for combustionfrom the fuel injector to the combustion chamber in the latter stage ofthe compression stroke in a light load/low speed range of the engine(Japanese Application Patent Laid-Open Publication NO. Hei 10-54246).

To put it more specifically, this direct injection engine is designed asfollows: A fuel injector is provided on the peripheral area of thecombustion chamber where swirl air flow is formed in a light load/lowspeed range. The distance from the injection nozzle of the fuel injectorto the inner surface of the cylinder placed face-to-face with theinjection nozzle is made longer than the distance for the arrival offuel spray by injection during the time from the start of fuel injectionto ignition. At the same time, the ignition plug is arranged so that theignition gap of the ignition plug electrode is located in the fuel sprayarea injected from the fuel injector. The distance from the injectionnozzle of the fuel injector to the ignition gap is made smaller than thedistance for arrival of fuel spray.

In this direct injection engine, fuel is injected from the fuel injectorinto the combustion chamber where the swirl gas flow is formed, in thelatter stage of the compression stroke in a light load/low speed rangeof the engine. As a result, stratified charge combustion is performed.At the time of ignition, spray fuel from the fuel injector does notreach the wall surface of the combustion chamber because of theconfiguration of the ignition plug, fuel injector and positionalrelationship between fuel spray angle and spray arrival distance.However, spray fuel is present around the ignition cap of the ignitionplug. This prevents spray from being deposited on the wall surface ofthe combustion chamber, and ensures stable ignition, thereby allowing aneffective stratified charge combustion to be performed.

In the direct injection engine of prior art, incidentally, stratifiedcharge combustion is carried out by swirl air flow in a light load/lowspeed range, and the above-mentioned action takes place as a result. Ina light load/high speed range, however, the piston traveling speed isincreased by high speed rotation if swirl air flow remains in thecombustion chamber. This makes it difficult to secure the time for sprayfuel evaporation. As a result, the fuel injection time must be advanced.However, if the fuel injection time is advanced, fuel spray angle willincrease due to low pressure in the combustion chamber, and spray fuelwill be deposited on the inner surface of the cylinder head. Thisproblem will cause another problem in stratified charge combustionoperation in a light load/high speed range.

To solve such problems in the direct injection engine of prior art,stratified charge combustion is performed by swirl air flow in a lightload/low speed range. Intake stroke injection is carried out in a heavyload/high speed range. At the same time, fuel is diffused throughcontrol of swirl ratio to provide uniform combustion. In a heavyload/high speed range, however, the sprayed fuel will be deposited onthe top surface of the piston if fuel is diffused through control ofswirl ratio to provide uniform combustion. This will make mixture withair difficult, and evaporation of spray fuel deposited thereon will bedelayed. Fuel will tend to be discharged from the engine together withexhaust gas, without being burnt.

This results in increased amount of the unburnt hydrocarbon (THC)contained in exhaust gas discharged from the engine, causingenvironmental issues. At the same time, it will deteriorate engineperformance and fuel economy.

The present invention has been made to solve these problems. Its objectis to provide a direct injection engine capable of direct injection offuel into the combustion chamber characterized in that discharge of gascontaining hazardous gas component such as THC can be reduced and fueleconomy can be improved by stratified charge combustion in the operationrange of low to high speeds.

DISCLOSURE OF THE INVENTION

To achieve the above object, the direct injection engine according tothe present invention is essentially characterized in that a tumble airflow is produced between the ignition plug located on the top of thecombustion chamber and the fuel injector located on the side of thecombustion chamber, and spray fuel is carried from the fuel injector tothe ignition plug by this tumble air flow.

The direct injection engine as another embodiment of according to thepresent invention comprises an ignition plug arranged in the verticalaxis direction of the cylinder, a fuel injector located on the axis lineinclined with respect to t e horizontal axis perpendicular to the axiscenter of the cylinder, and an intake air control means. The intake aircontrol means generates a tumble air flow in the combustion chamber, andthe fuel injector discharges fuel from the intake air side in thecombustion chamber toward the exhaust side. The ignition plug and thefuel injector are arranged in such a way that an angle β formed by avirtual straight line connecting between the ignition plug electrode andfuel injection point of the fuel injector and a horizontal axis line(X), and an spray top end angle γ (elevation angle) formed between thespray outer edge of spray fuel and horizontal axis line are within therange γ=β±5 deg. As a fuel injector, the one equipped with aswirl-generating element upstream from the valve body is suitably used.

The penetration of spray fuel is preferred to be longer on the ignitionplug side than on the piston side.

To achieve the above-mentioned object, the present invention is designedin such a way that the fuel spray injected from the fuel injector iscarried to the ignition plug by the tumble air flow which reaches theplug after rising from below the fuel injector along the wall surface ofthe intake air side in the combustion chamber (called tumble guidemethod).

To put it more specifically, the fuel injector is designed to ensurethat fuel is injected 3.15 msec. before ignition timing of the ignitionplug. The fuel injector is also configured so that fuel is injected at80 deg. before top dead point when mean effective pressure in thecombustion chamber is 350 KPa at the engine speed of 3200 rpm.

The direct injection engine according to the present invention designedto have the above-mentioned configuration reduces the amount of fueldeposited on the top surface of the piston and inner wall of thecylinder block, and improves ignition property of the ignition plug.

In other words, spray fuel is carried by tumble air flow over a shortdistance from the fuel injector to the ignition plug on the side of thecylinder. This reduces the amount of spray fuel deposited on the topsurface of the piston and inner wall of the cylinder block. It alsoincreases spray fuel density close to the ignition plug, therebyimproving ignition property by the ignition plug.

As a result, the direct injection engine according to the presentinvention allows stratified operations to be performed over an extensiverange from the idling range to the high speed range. It also reduces theamount of spray fuel deposited on the upper surface of the piston andinner wall of the cylinder block. This, in turn, reduces the amount ofTHC contained in exhaust gas, improves the purification rate, andimproves fuel economy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective conceptual diagram representing one embodimentof a direct injection engine according to the present invention;

FIG. 2 is a drawing representing the status of the forward tumble airflow sucked into the combustion chamber of the direct injection engineof FIG. 1, and the status of fuel spray;

FIG. 3 is a drawing representing the positional relationship between theignition plug and fuel injector of the direct injection engine of FIG.1, spraying state of the fuel injector, and the positional relationshipbetween the ignition gap and ignition plug electrode;

FIG. 4 is a drawing illustrating how to photograph spray fuel injectedfrom the fuel injector and how to calculate the fuel spray angle θ andpenetration length L from the photographed spray fuel image, wherein (a)shows the photographing method, and (b) illustrates the calculationmethod;

FIG. 5 is a drawing representing the relationship between changes inengine operation states (speed and cylinder internal pressure) and theoptimum fuel injection time, wherein (a) shows the relationship betweenengine speed and optimum injection time, and (b) indicates the optimuminjection time as viewed from the cylinder internal pressure and crankangle;

FIG. 6 is a drawing representing how the optimum form of spray condition(specifications) is derived from the relationship between the fuel topend angle γ and penetration length L through experiment and simulationusing the direct injection engine of FIG. 3;

FIG. 7 is a drawing representing the form of spraying from multiple fuelinjectors, different from that of spraying of prior art, wherein (a)shows straight spraying, (b) straight spraying with deviated density and(c) deviated spraying;

FIG. 8 is a drawing showing the direct injection engine of FIG. 1equipped with a fuel injector of deviated spraying mode where deviationis found in distribution of fuel spraying density;

FIG. 9 is a drawing showing the direct injection engine of FIG. 1equipped with a fuel injector of straight (symmetrical) spraying modewhere distribution of fuel spray density is uniform on thecircumference;

FIG. 10 is a drawing showing the relationship between ignition-enabledtime T and conical fuel spray angle θcon with respect to penetrationlength L of spray fuel, wherein (a) shows the relationship betweenpenetration length L and ignition-enabled time T, and (b) depicts therelationship between penetration length L and conical fuel spray angleθcon; and

FIG. 11 is a drawing representing the direct injection engine equippedwith the fuel injector for spraying fuel at conical fuel spray angle θpwhere the inner wall angle of the engine head is θwall.

BEST FORM OF EMBODIMENT OF THE INVENTION

The following describes one embodiment of the direct injection engineaccording to the present invention with reference to drawings:

FIG. 1 is a perspective conceptual diagram representing a directinjection engine according to the present embodiment. A cylinder block 2is mounted on the bottom of each cylinder of an engine body 1, and acylinder head 3 is mounted on the top of the cylinder block 2.

A piston 4 having the top surface designed in an almost flat shape isprovided inside the cylinder block 2 slidably in the vertical direction,and the space between the cylinder block 2 and the piston 4 is formed asa combustion chamber 5. The cylinder head 3 is designed as a pent roof,and the cylinder head 3 is connected with two intake manifolds 6 and 6opening into the combustion chamber 5, and two exhaust pipes 7 and 7.Intake valves 8 and 8 are respectively arranged on intake manifolds 6and 6 at the connection with the cylinder head 5, and exhaust valves 9and 9 are respectively arranged on the exhaust pipes 7 and 7.

A fuel injector 10 for injecting fuel directly into the engine cylinderis installed between two intake valves 6 and 6 of the cylinder head 5,with its injection nozzle (injection point) 10 a facing the combustionchamber 5. The fuel injector 10 is a high pressure swirling fuelinjector designed to have such a shape that a conical form at thespecified spray angle is obtained by giving a swirling force to thespray fuel. The fuel spray angle of the injected spray fuel tends todecrease with the increase in the pressure inside the combustion chamber4. An ignition plug 11 is arranged at the central position on top of thecylinder head 5, with an electrode 11 a forming an ignition gap facingthe combustion chamber 5.

The intake valves 8 and 8 and exhaust valves 9 and 9 are moved in thevertical direction by the cam shaft (not illustrated) positioned on thetop of cylinder head 3, thereby opening or closing the communicatingvalve holes between the intake manifolds 6 and 6 and exhaust pipes 7 and7 formed on the cylinder head 3. Through a connecting rod 4 a, thepiston 4 is connected and interlocked with the crank shaft (notillustrated) which is shaft-supported rotatably on the bottom of thecylinder block 2. As the piston 4 is moved inside the cylinder block 2in the vertical direction by the operation of the engine, the crankshaft is driven and rotated.

Two intake manifolds 6 and 6 upstream from intake valves 8 and 8 areprovided with rectifier plates 12 and 12 for separating the intake flowpath of intake manifolds 6 and 6 into top and bottom. Flow dividingvalves 13 and 13 are arranged upstream from the rectifier plates 12 and12. The flow dividing valves 13 and 13 comprise a valve shaft 13 a andvalve body 13 b, and are arranged to ensure that the valve body 13 b ismoved within the range of 90 degrees from the position immediately belowto the immediate side by rotating the valve shaft 13 a. The flowdividing valves 13 and 13 are used to control the velocity and directionof air flow formed in the combustion chamber 4. When the air flowvelocity is to be increased, the bottom flow paths 6 a and 6 a of theflow paths separated into two parts are blocked by the flow dividingvalves 13 and 13. Then the area of the flow paths in the intakemanifolds 6 and 6 is decreased, namely, a forward tumble air flow isformed in the combustion chamber 5. When the velocity of air flow formedin the combustion chamber 5 is not to be increased, or much air is to besucked from the combustion chamber 5, the flow dividing valves 13 and 13are opened, and the bottom flow paths 6 a and 6 a are released.

FIG. 2 shows the status of the tumble air flow sucked into thecombustion chamber 5 of the direct injection engine of according to thepresent embodiment, and the status of fuel spray. When flow dividingvalve 13 is closed and air flow is sucked into the combustion chamber 5only from the top flow path 6 b on the intake manifold 6, the state offorward tumble air flow shown by the arrow A occurs in the combustionchamber 5. This air flow moves on the top surface of the piston 4 andrises along the side surface (cylinder side surface) of the combustionchamber on the intake valve side. The fuel injected from the fuelinjector 3 produces a deformed conical spray which is longer on the plugside and shorter on the piston side, as in the case of spray fuel B. Theconical spray fuel B is carried by the tumble air flow to the ignitiongap of the electrode 11 a of ignition plug 11.

The tumble air flow A rises from the bottom of the spray fuel B, andspray fuel B is placed in the direction of the tumble air flow A. Sprayfuel B is carried by the tumble air flow A moving from the fuel injector10 to the ignition plug to reach the electrode 11 a of the ignition plug11. For example, when the engine speed is equivalent to 1400 rpm, thespray fuel reaches the electrode 11 a of the ignition plug 11 3.15 msecafter fuel is injected from the fuel injector 10.

(1) in FIG. 2 indicates that the fuel is injected prior to time of plugignition.

(2) shows that fuel is carried to the plug by tumble air flow.

Under the condition of (2), ignition signal is just sent to the plug,and ignition timing is reached.

To put it more specifically, when mean effective pressure in thecombustion chamber is 320 KPa (kilo-Pascal) at the engine speed of 1400rpm, fuel is injected at 70 deg. before top dead point, and ignitiontiming is at 35 deg. before top dead point.

When mean effective pressure in the combustion chamber is 350 KPa at theengine speed of 3200 rpm, fuel is injected at 80 deg. before top deadpoint, and ignition timing is at 30 deg. before top dead point.

In both cases, fuel is injected about 3 msec. before ignition timing.This time has been measured in various operation ranges, and it has beenrevealed that injection of fuel 3.0 to 3.15 msec. before issatisfactory.

FIG. 3 shows the positional relationship between the ignition plug 11and fuel injector 10 of the direct injection engine according to thepresent embodiment, and the positional relationship between theinjection nozzle (injection point) 10 a of the fuel injector 10 and theignition gap (ignition point) of electrode 11 a of ignition plug 11.

The ignition plug 11 is arranged in the vertical direction with its axiscenter Y in the longitudinal direction matching with that of the engineblock 2. The fuel injector 10 is arranged with its axis center zinclined by angle (injector installation angle) α with respect to theaxis line X at a right angle to the axis center Y and passing throughthe axis center Y, where the injection nozzle 10 a of the fuel injector10 is used as a reference point. The ignition gap (ignition point) ofthe electrode 11 a of the ignition plug 11 is positioned at angle 62with respect to the axis line X where the injection nozzle (injectionpoint) 10 a of the fuel injector 10 is used as a reference point. Theignition gap of the electrode 11 aand the injection nozzle (injectionpoint) 10 a are located so that there is a positional distance l betweenthem.

Spray injected from the fuel injector 10 has a deflected conical form,and is injected at a fuel spray angle θ (angle formed between the axiscenter Z of the fuel injector 10 and spray top edge). The angle formedbetween the axis line X and spray top edge is assumed as a spray top endangle γ, and the length of deflected conical spray is assumed aspenetration (distance for spray arrival) L. spray is generated so thatthis penetration is longer than positional distance l.

FIG. 4 illustrates how to photograph spray fuel injected from the fuelinjector and how to calculate the fuel spray angle e and penetrationlength L of the photographed spray fuel image, wherein (a) shows thephotographing method, and (b) illustrates the calculation method;

The following describes the method of photographing: A chamber allowinga specified pressure to be created therein, a fuel injector 10 forinjecting fuel into this chamber and a high-speed camera are used inthis case. Fuel from a fuel tank is injected (e. g. injection pulsewidth of lms) at a specified pressure (e.g. 7 MPa) from the fuelinjector 10 into the chamber to which specified pressure (e.g. 0.6 MPa)is applied, and a conical spray fuel is formed. In the meantime, laserbeam is applied into the chamber from argon laser. The state of conicalspray fuel 3.6 msec. after injection is started from the fuel injector10 is photographed by the high-speed camera to get a spray fuel image.The specified pressure of the fuel injected from the fuel injector 10 isequivalent to the pressure of fuel injected into the engine. Thespecified pressure in the chamber is equivalent to the pressure insidethe cylinder when the fuel is injected into the cylinder of the engine.Photograph is taken without air flow in this chamber.

(b) shows how to calculate the fuel spray angle θ and penetration lengthL from the spray fuel image obtained from the photographing method givenin (a). Measurement is made of the angle e formed between edge F of theconical spray fuel on the ignition plug side and axis center Z on theline W perpendicular to axis center Z 25 mm from the injection nozzle 10a of the fuel injector 10. Namely, fuel spray angle θ is measured.Furthermore, penetration length L is measured as a distance from theinjection nozzle 10 a of the fuel injector 10 to the tip in thedirection of injection.

In this way, if the fuel spray angle θ of the fuel injector 10 isdetermined, angles α and 62 are predetermined by each cylinder, as shownin FIG. 3. So the spray top end angle γ can be determined from θ−α=γ.

FIG. 5 represents the relationship between changes in engine operationstates (speed and cylinder internal pressure) and the optimum fuelinjection time, wherein (a) shows the relationship between engine speedand optimum injection time, and (b) indicates the optimum injection timeas viewed from the cylinder internal pressure and crank angle. (a)indicates that the optimum injection time is delayed when the enginespeed is high, and (b) shows that cylinder internal pressure is highwhen the crank angle at the optimum time for fuel injection is delayed,while the pressure is low when the crank angle at the optimum time forfuel injection is advanced.

Furthermore, the spray angle and penetration (spray length) of the fuelsprayed from the general fuel injector depend on the cylinder internalpressure. The higher the cylinder internal pressure, the smaller thespray angle and penetration. This suggests that the preferred fuelinjector to cope with various states is the one capable of sprayingwithout being affected by the changes in cylinder internal pressure. Toput it more specifically, such preferred valves include those capable of(1) solid spraying in conical form where fuel including the innerportion is sprayed, (2) spraying in porous conical form, or (3) powerfulspraying in the direction of the electrode of ignition plug 11.

FIG. 6 represents how the optimum form of fuel spray condition(specifications) is derived from the relationship between spray top endangle γ and penetration length L through experiment and simulation usingthe direct injection engine where the relationship between the ignitionplug 11 and the fuel injector 10 is as given in FIG. 3.

In experiment and simulation, use was made of a direct injection enginewherein the angle β formed between the ignition gap (ignition point) ofthe electrode 11 a of the ignition plug 11 and the injection nozzle(injection point) 10 a of the fuel injector 10 was 0, and the distance lbetween the ignition gap of the electrode 11 a and the injection nozzle(injection point) 10 a was 40 mm. Operation was performed at an enginespeed of 1600 mm, cylinder internal pressure Pi of 320 kPa and air/fuelratio A/F of 35, with tumble air flow in the combustion chamber 5 forthis experiment and simulation.

According to the result of the experiment using an actual apparatus, thestable combustion area can be ensured when the spray top end angle γ isin the range from −1 to 10 deg. According to the result of simulation,however, fuel may be deposited on the intake valve during injection inthe intake stroke if the spray top end angle γ is 5 deg. or more. In thecase of experiment using an actual apparatus, the combustion area isoutside the stable area if the spray top end angle γ is −1 deg. Insimulation, spray fuel can be raised to the ignition plug 11 to reachthe spark gap of the electrode 11 a of the ignition plug 11 bygenerating a tumble air flow in the cylinder in an appropriate state. Sothe range of the spray top end angle γ of up to about −5 can be set asthe optimum fuel spray condition (specification). Furthermore, insimulation, fuel is anticipated to deposit on the inner wall of theexhaust valve cylinder when the penetration length L is 64 mm or more.So the optimum fuel spray condition (specification) is reached thepenetration length L is below 64 mm. Furthermore, if there is no tumbleair flow, the penetration length L is required to be greater than thedistance 1 of 40 mm between the spark gap 11 of the electrode andinjection nozzle. According to the result of simulation, penetrationlength L should be about 45 mm or more under the optimum fuel spraycondition.

When consideration is given to the fuel carried by the tumble air flow,the excess amount of fuel will pass by the plug at the time of ignitionif the conditions are better.

In other words, according to the result of experiment and simulation,the spray top end angle γ in the optimum fuel spray condition isrequired to be within the range of β±5 (where β denotes an angularposition of the spark gap (ignition point) of the electrode of theignition plug when the injection nozzle of the fuel injector is used asa reference point), when operation is performed with tumble air flow inthe combustion chamber of the direct injection engine. In this case, itis also required that penetration length L of spray fuel be greater thanthe distance l of 40 mm between the spark gap of the electrode andinjection nozzle (injection point). The approximate penetration length Lshould be within the range from 40 to 45 mm.

In the measurement of FIG. 4, it is possible to check from γ=±5 to seeif the specific spray top end angle γ is under the optimum fuel sprayconditions or not, if the spray top end angle γ of the specific fuelinjector is determined.

FIG. 7 represents the form of spraying from multiple fuel injectors,different from that of commonly used spraying mode, wherein (a) showsstraight spraying, (b) straight spraying with deviated density and (c)deviated spraying. It shows the state of spraying at a conical sprayangle θ. In (a) straight spraying, fuel is sprayed to an object in aconical form with the axis center Z of the fuel injector as a center. In(b) straight spraying with deviated density, fuel is sprayed to anobject in a conical form with the axis center Z of the fuel injector asa center, but spraying length is not symmetrical. In (c) deviatedspraying, fuel is sprayed unsymmetrically in a conical form with theaxis center Z of the fuel injector as a center. Spraying length is notsymmetrical, either.

From the layout relationship between the ignition plug 11 and the fuelinjector 10 shown in FIG. 2, in other words, relationship between α andβ it can be appreciated that, as the ignition point of the ignition plug11 is higher (as the angle β is greater) or more fuel is injected fromthe fuel injector 10 down to the cylinder block 2 (as the angle β isgreater), the fuel injector is required to inject fuel at a wider angle(greater conical spray angle θcon) in order to satisfy γ=β±5. If fuel ata wider angle is injected, spray fuel per unit volume is less dense, sofuel at the ignition point of ignition plug 11 is anticipated as lessdense. Thus, use of a fuel injector of deviated spraying is moreeffective when relationship between angles α and β, namely, α+β isgreater. Conversely, if α+β is smaller, a fuel injector of straightspraying can be used.

Accordingly, when conical spray angle in various spraying modes (a) to(c) of FIG. 7 is θcon, use of (c) deviated spraying is effective in thecase of θcon/2>40 deg., wherein spraying of partially different densityis provided. When θcon/2≦40 deg., use of a fuel injector of eachspraying mode in (a) to (c) is preferred.

FIGS. 8 and 9 show spraying in the case of direct injection enginesequipped with the fuel injectors characterized by different fuelspraying modes. FIG. 8 represents a direct injection engine equippedwith a fuel injector of deviated spraying mode where deviation is foundin distribution of fuel spraying density. FIG. 9 represents a directinjection engine equipped with a fuel injector of straight (symmetrical)spraying mode where distribution of fuel spray density is uniform on thecircumference.

In the deviated spraying mode of FIG. 8, spray density is high in thedirection of the ignition plug, so denser fuel is likely to be injectedto the position around the gap of the electrode of the ignition plug. Inthe straight (symmetrical) spraying mode shown in FIG. 9, denser fuel isnot spread around the gap of the electrode of the ignition plug. Sincethe density of fuel sprayed toward the piston is higher than that indeviated spraying mode, fuel tends to deposit on the top surface of thepiston. This may lead to an increase in the amount of HC contained inthe exhaust gas.

From this, it is apparent that the fuel injector of deviated sprayingmode is basically preferred when used in the direct injection engineaccording to the present embodiment.

FIG. 10 represents the relationship between ignition-enabled time T andconical fuel spray angle θcon with respect to penetration length L ofspray fuel, wherein (a) shows the relationship between penetrationlength L and ignition-enabled time T, and (b) depicts the relationshipbetween penetration length L and conical fuel spray angle θcon.

Penetration length L is limited in its permissible length. When thecritical length P is exceeded, there will be no ignition-enabled timeand ignition failure may occur. Penetration length L is inverselyproportional to conical fuel spray angle θcon. If penetration length Lis greater, fuel spray angle θcon. must be reduced. Conversely, ifpenetration length L is smaller, conical fuel spray angle θcon must beincreased. Furthermore, since the penetration length L has a criticallength P in relation to ignition-enabled time, it is subjected to therestriction of conical fuel spray angle θcon due to critical length P.The fuel spray angle θcon smaller than conical fuel spray angle θp concorresponding to critical length P is not suited to use in the directinjection engine according to the present embodiment.

FIG. 11 represents the direct injection engine equipped with the fuelinjector 10 for spraying fuel at conical fuel spray angle θp where theinner wall angle of the engine head is θwall. It illustrates how to setthe fuel spray angle θ with respect to the conical fuel spray angle θpand the inner wall angle of the engine head is θwall.

When the fuel spray angle θ is smaller than θ/2, the ignition time istoo short, and ignition error is likely to occur. At the same time, whenfuel spray angle θ is greater than θwall, spray fuel may deposit on theinner wall of the engine head. This may lead to the fuel beingdischarged as unburnt hydrocarbon (HC) together with exhaust gas.

For this reason, fuel spray angle θ must be set within the range fromθp/2<θ<θwall.

The above describes one embodiment of the present invention. The presentinvention is not restricted to this embodiment. Various designingmodifications are possible without departing from the spirit of theinvention described in WHAT IS CLAIMED.

Applicability in Industry

As can be seen from the above description, the direct injection engineaccording to the present invention is characterized in that spray fuelis received by air flow due to tumble flow and is shifted to theignition plug on the side of the cylinder head. This reduces the amountof fuel deposited on the upper surface of the piston and inner wall ofthe cylinder block. It also increases the density of the spray fuelclose to the ignition plug, thereby improving the ignition by ignitionplug.

The direct injection engine according to the present invention allowsstratified operations to be performed over an extensive range from theidling range to the high speed range. It also reduces the amount ofspray fuel deposited on the upper surface of the piston and inner wallof the cylinder block. This, in turn, reduces the amount of THCcontained in exhaust gas, and improves the purification rate and fueleconomy.

What is claimed is:
 1. A direct injection engine comprising: a cylinderhead having a conically-shaped face, an ignition plug arranged on thetop of a combustion chamber, positioned at an apex point of theconically-shaped face, and installed at a substantial center of thecylinder head, a fuel injector located on a side of said combustionchamber and installed in a vicinity of an intersection point between thecylinder head and a cylinder block, and an intake air control meansinstalled on an intake manifold, wherein said intake air control meansgenerates a tumble air flow rising from the bottom of said fuel injectorto said ignition plug in said combustion chamber, wherein said fuelinjector is configured to inject fuel spray from the intake side in saidcombustion chamber to the exhaust side, thereby supplying said fuelspray between said ignition plug and said tumble air flow, wherein, withrespect to a line which passes through an injection point of the fuelinjector and intersects at a substantially right angle with a centerline of a cylinder, the fuel injector is installed so as to be inclinedalong a central axial line of the fuel injector toward the piston side,and wherein, when the fuel spray injected from the fuel injector issectionally crossed with a plane which includes a spark point of theignition plug and the injection point of the fuel injector, the ignitionplug is positioned between the line which passes through the injectionpoint and the face of the cylinder head.
 2. The direct injection engineaccording to claim 1, wherein the ignition plug is arranged along thevertical axis center of the cylinder, wherein the central axial line isinclined with respect to the line which passes through the injectionpoint, wherein said ignition plug and said fuel injector are arranged insuch a way that an angle β formed by a virtual straight line connectingbetween the spark point of said ignition plug and the injection point ofsaid fuel injector and said line which passes through the injectionpoint, and wherein a spray top end angle γ formed between a spray outeredge of said fuel spray and said line which passes through the injectionpoint are within the range of γ=β+5 deg.
 3. The direct injection engineaccording to claim 1, wherein said fuel injector has a swirl generatingelement.
 4. The direct injection engine according to claim 1, whereinsaid fuel injector has a penetration which is long in the direction ofsaid ignition plug and short in the direction of a piston.
 5. The directinjection engine according to claim 1, wherein a distance for arrival ofsaid fuel spray is set greater than a layout distance between theinjection point of said fuel injector and the spark point of saidignition plug.
 6. The direct injection engine according to claim 5,wherein said distance for arrival of the fuel spray is within the rangefrom about 1.125 to 1.6 times the layout distance.
 7. The directinjection engine according to claim 1 wherein a fuel spray angle θ ofthe fuel spray is set within θp/2<θ<θwall in a relationship between fuelinjection angle θp of a permissible critical distance duringignition-enabled time regarding a distance for arrival of spray fuel anda face angle θwall of the cylinder head.
 8. The direct injection engineaccording to claim 1 wherein said fuel injector is arranged to ensurethat spray density distribution is deviated and a portion of higherdensity is sprayed to the spark point of said ignition plug.
 9. Thedirect injection engine according to claim 8, wherein the fuel spray issprayed in a conical form and at a conical spray angle θcon, and whereinsaid conical spray angle is within the range of θcon/2>40 deg.
 10. Acombustion method for a direct injection engine including a cylinderhead having a conically-shaped face, an ignition plug arranged on thetop of a combustion chamber, positioned at an apex point of theconically-shaped face, and installed at a substantial center of thecylinder head, a fuel injector located on a side of said i combustionchamber and installed in a vicinity of an intersection point between thecylinder head and a cylinder block, and an intake air control meansinstalled on an intake manifold, the method comprising: generating atumble air flow rising from the bottom of said fuel injector to saidignition plug in said combustion chamber with said intake air controlmeans, and causing fuel spray injected from said fuel injector to risefrom the bottom of said fuel injector along a wall surface on an intakeair side in said combustion chamber and to be carried by said tumble airflow from said fuel injector to said ignition plug so that said fuelspray reaches said ignition plug by the time of ignition of saidignition plug, wherein, with respect to a line which passes through aninjection point of the fuel injector and intersects at a substantiallyright angle with a center line of a cylinder, the fuel injector isinstalled so as to be inclined along a central axial line of the fuelinjector toward the piston side, and wherein, when the fuel sprayinjected from the fuel injector is sectionally crossed with a planewhich includes a spark point of the ignition plug and the injectionpoint of the fuel injector, the ignition plug is positioned between theline which passes through the injection point and the face of thecylinder head.
 11. The combustion method for a direct injection engineaccording to claim 10, wherein said fuel injector is designed to sprayfuel 3 msec. before the time of ignition of the ignition plug.
 12. Thecombustion method for a direct injection engine according to claim 10,wherein said fuel injector is designed to inject fuel at 80 deg. beforetop dead point when mean effective pressure in the combustion chamber is350 KPa at the an engine speed of 3200 rpm.
 13. The combustion methodfor a direct injection engine according to claim 10, wherein theignition plug is arranged along the vertical axis center of thecylinder, wherein the central axial line is inclined with respect to theline which passes through the injection point, wherein said ignitionplug and said fuel injector are arranged in such a way that an angle βformed by a virtual straight line connecting between the spark point ofsaid ignition plug and the injection point of said fuel injector andsaid line which passes through the injection point, and wherein a spraytop end angle γ formed between a spray outer edge of said fuel spray andsaid line which passes through the injection point are within the rangeof γ=β±5 deg.